1. Field of the Invention
The present invention relates to a booster converter circuit for a vehicle which causes an inductive element to generate an induced electromotive force by switching control, to output a voltage including the induced electromotive force added to an output voltage of a battery.
2. Description of the Related Art
Motor-driven vehicles such as electric cars, hybrid cars, and the like are widely used. A motor of the motor-driven vehicle is rotated by electrical power supplied from a battery and drives wheels. An adjustable speed control of the motor-driven vehicle is achieved by adjusting electrical power to be supplied to the motor according to an operation of an accelerator, a brake, or the like. Therefore, a booster converter circuit for adjusting electric power to be supplied from the battery to the motor is mounted on the motor-driven vehicle.
The booster converter circuit includes an inductor for boosting the battery voltage. The booster converter circuit causes the inductor to generate the induced electromotive force by switching-controlling a current flowing from the battery to the inductor, and charges an output capacitor at a voltage including the induced electromotive force added to the battery voltage. Then, an inter-terminal voltage of the output capacitor is outputted as a boosted voltage. The boosted voltage is adjustable by changing the timing of switching the current flowing to the inductor.
A motor is connected to the output terminal of the booster converter circuit via an inverter circuit which converts a DC voltage to an AC voltage. In this configuration, electrical power supplied from the battery to the motor can be adjusted by adjusting the boosted voltage of the booster converter circuit.
A control unit which controls the booster converter circuit determines a target boosted voltage on the basis of a driving operation. Then, the switching timing of the current flowing in the inductor is adjusted so that the boosted voltage approaches a target boosted voltage. The motor is rotated by electrical power controlled in this manner and drives wheels. Accordingly, the adjustable speed control of the motor-driven vehicle on the basis of the driving operation is achieved (see JP-A-2006-115635, JP-A-2007-166875, and JP-A-2004-112904).
The boosted voltage approaches the target boosted voltage and the charging and discharging current of the output capacitor is reduced under the control of the control unit. Accordingly, a current flowing in the booster converter circuit is reduced according to the charging and discharging of the output capacitor.
When a load on the wheels is changed, a current flowing in the motor is changed. Under such conditions as well, the control unit controls the booster converter circuit so that the boosted voltage approaches the target boosted voltage. Accordingly, a current according to the charging and discharging of the output capacitor flows in the booster converter circuit.
Therefore, when the current flowing in the motor is suddenly changed due to sudden variations of the load caused by slipping of the wheels or the like, a large current flows in the booster converter circuit. Therefore, there is a problem that it is necessary to provide the booster converter circuit with a component whose allowable current value is high by taking increase in current due to the load variations into consideration, so that the manufacturing cost of the booster converter circuit is increased.